In packaging technique, packages of the non-returnable type have been is use for a long time which are manufactured from a material which consists of a carrier layer of cardboard or paper and outer and inner coatings of thermoplastics. Frequently the packing material in such packages is also provided with additional layers of other material, e.g. aluminium foil or plastic layers other than those mentioned.
The composition of the packing material is intended to create the optimum product protection for the goods which are to be packed, and to impart sufficient mechanical protection for the product in the package and adapting it so that it can be readily handled by the user of the package. In order to achieve mechanical rigidity so as to provide mechanical protection for the contents and make it possible for the package to be of such rigid form that it can be handled and gripped by hand without difficulty, the packages of this type are often provided with a carrier layer of paper or cardboard which gives the package rigidity of form and affords mechanical protection. Such a carrier layer, however, is permeable to gases or liquids and the rigidity of the material disappears if the material is subjected to moisture or if liquid is absorbed into the material. To make the material satisfactorily impermeable to liquids, it is most frequently laminated with a plastic material, and if this plastic material is thermoplastic, the plastic layers can be sealed to each other with the help of heat and pressure. In this manner, the packaging container can be sealed and given permanent form by the sealing of overlapping, plastic coated material panels to each other in a tight and mechanically durable and strong seal.
Packing containers of the type referred to here are manufactured either from blanks punched out beforehand or from a continuous web which has been prepared with suitable decoration and with a crease line pattern facilitating the folding. The packing containers are manufactured from such a web by joining together the longitudinal edges of the web in an overlap joint so as to form a tube which is subsequently filled with the intended contents and divided into closed container units by means of repeated transverse sealing of the tube perpendicularly to the longitudinal axis of the tube. After suitable folding of the packing material in the tube the material in the said container units is converted to the desired geometrical shape, usually a parallelepiped, by providing the tube with longitudinal folding lines and with double-walled triangular lugs at the corners of the packing container.
Whether the packing containers are manufactured from blanks produced beforehand or from a continuous web, the material, for practical reasons, will be of uniform thickness and in order to make it possible to achieve the desired rigidity of form the paper or cardboard layer is relatively thick in relation to the remaining layers included in the laminate. This means that the combined layers which are produced in the forming and sealing of the package bring about appreciable local thickenings and that leakage problems may arise at the transitions between one portion with multiple material thickness and one with single material thickness. Such leakage problems are accentuated especially at intersections between joints where each joint region presents double or multiple material thickness. At such intersections which in general are usually called "crosses", leakage channels can easily occur which may cause slight liquid leakage or which in aseptic packages may cause infection of the sterile contents of the package.